[s-cars] 93 S4 heater issues

[Tom Green]

Sam,

The heater control valve usually has a lot of resistance and is hard  
to move the lever
up by hand.  It illustrates the strength of the vacuum system when  
given a little
mechanical advantage, so I am surprised you can move the valve with  
mouth suction.
You may want to remove the valve to verify it is intact and operating  
properly.  This is
a very inexpensive part on the aftermarket here and all I have bought  
are OEM parts
with the Audi logo marked over.  Just be careful removing any parts.   
The hoses are
usually stuck tight to the plastic nipples so it is easy to break  
them.  The heater inlet
nipples are plastic as well, and the small rubber connector from the  
valve to the
heater core inlet is a high value part (has a plastic air bleed screw  
on top) so take care.
It should be obvious that the small nipples for the vacuum connectors  
are fragile as
well.

Check out the knowledge base and FAQ section at audifans.com.  There  
is a lot of
information about the system as well as repair experience on that  
site.  You can see
the inlet and outlet hoses for the heater under the plenum cover.   
The outlet is below
the inlet with the vacuum controlled heater valve so you can verify  
that heat flows into
and out of the heater core by feeling the hose temperature with the  
system in the heat
mode as well as observe the lever on the side of the water tap move.   
Look at the
diagnostic procedure for the HVAC.  If any of the flaps and valves  
are not operating,
error codes will be displayed on the automatic climate control head.   
I would clear
any codes and operate the system a while to see if they return before  
replacing parts.

If the heater core is plugged, there are details for replacing it on  
audifans as well, but
let's hope we don't have to go there yet.

Tom

> Date: Wed, 25 Apr 2007 15:58:07 +1200
> From: Sam Clarkson <sam at edgetoedge.co.nz>
> Subject: [s-cars] 93 S4 heater issues
> To: s-car-list at audifans.com
> Message-ID: <CFD21E9A-C2E5-4F84-B1E4-C589F9485ADA at edgetoedge.co.nz>
> Content-Type: text/plain;	charset=US-ASCII;	delsp=yes;	format=flowed
>
> Team
> No heat, winter approaching here on the top side of the planet. I've
> pulled off and sucked on the vac line to the water tap and its moving/
> working fine. There is good vac to the solenoid that controls the
> tap, even when the engine's been off for hours, so no vacuum issues.
> Can I swap that solenoid with the other one (what does it do) to
> test?. Can I test voltage to it, what readings am I looking for at
> hot and cold? What else?
> Love you always
>
>
> Sam Clarkson